1. Field of the Invention
The present invention relates to a light guide member and an illumination apparatus for guiding light emitted from a plurality of light-emitting devices to an object, and irradiating the object, and an image capturing apparatus for capturing an image of the object using the same, and more particularly a light guide member and an illumination apparatus for uniformly irradiating a predetermined range of the object with light emitted from a plurality of light-emitting devices functioning as point light sources, and an image capturing apparatus using the same.
2. Description of the Related Art
An image capturing apparatus for capturing an image in a predetermined range of an object by irradiating the object with uniform light is widely used. In an image processing system using an image captured by such the image capturing apparatus, a sharp image is particularly required.
For example, with the development of biometric technologies in recent years, there have been provided a variety of apparatuses for personal identification, which captures an image of a portion of a human body by which an individual can be distinguished and recognizes a feature of the human body, for example, fingerprints of limbs, eye retinas, face and blood vessels.
In particular, blood vessels and skin patterns of a palm and a finger are suitable for reliable personal authentication, because a relatively large amount of personal feature data may be obtained therefrom. Further, it is believed that the patterns of blood vessels (veins) do not change from the time of an embryo throughout the lifetime of any person, and that no identical pattern exists among any persons without exception, which are therefore suitable for personal authentication. FIGS. 19 through 22 show explanation diagrams of the conventional blood vessel image authentication technique. As shown in FIG. 19, at the time of registration or authentication, a user puts a palm of a hand 110 close to an image capturing apparatus 100. The image capturing apparatus 100 emits a near infrared ray, and irradiates the palm of the hand 110. The image capturing apparatus 100 receives the near infrared ray reflected from the palm of the hand 110 by a sensor.
As shown in FIG. 20, hemoglobin in the red corpuscle flowing in a vein loses oxygen. Such the hemoglobin (deoxidized hemoglobin) absorbs the near infrared of the vicinity of 760 nm in wavelength. Accordingly, when the palm is irradiated with the near infrared, reflection is reduced in a portion in which a vein exists. Thus, by the degree of strength of the reflected near infrared, the location of veins can be recognized.
As shown in FIG. 19, first, the user registers a vein image data of the own palm into a server or a card, using the image capturing apparatus 100 shown in FIG. 19. Next, to perform personal authentication, the user makes the vein image data of the own palm to be read, using the image capturing apparatus 100 shown in FIG. 19.
The personal authentication is performed by collating the registered vein image data, which is extracted using a user ID, with a vein pattern in the collation vein image being read above. For example, in the case of the collation of the vein patterns between the registered image and the collation image as shown in FIG. 21, the person is authenticated as genuine. Meanwhile, in the case of the collation of the vein patterns between the registered image and the collation image as shown in FIG. 22, the person is not authenticated as genuine (see Japanese Unexamined Patent Publication No. 2004-062826, FIGS. 2-9).
For such the biometric authentication or the like, it is necessary to image an object (a portion of a human body in case of the biometric authentication) in a non-contact manner. For this purpose, the image capturing apparatus 100 emits light producing uniform light intensity in a certain image capturing range (distance and area), receives the reflected light of the above image capturing range by a sensor, and outputs a captured image signal as an electric signal.
FIGS. 23 and 24 show explanation diagrams of the conventional image capturing apparatus. As shown in FIGS. 23 and 24, the image capturing apparatus 100 includes an imaging unit 120 at the center, and in the periphery thereof, a plurality of light-emitting devices 130-1 to 130-8. The dotted lines shown in FIG. 23 represent the range of the light having uniform intensity emitted from an individual light-emitting device among the plurality of light-emitting devices 130-1 to 130-8.
As such, by disposing a plurality of (here, eight) point light sources in the periphery of imaging unit 120, the imaging range of the imaging unit 120 can be irradiated with the light of uniform intensity. Meanwhile, imaging unit 120 includes a photoelectric conversion unit 122 such as a CMOS sensor, and an optical system 124 such as a lens. Since the photoelectric conversion device, which is a plane photodetector device, has a predetermined light receiving area, a predetermined optical distance is required to guide the reflected light of the image capturing range onto the light-receiving plane of the photoelectric conversion device 122. For this purpose, a lens 124 such as a fisheye lens is disposed between the photoelectric conversion unit 122 and the object, so that an image of the predetermined image capturing range is projected onto the light-receiving plane of photoelectric conversion device 122.
Thus, conventionally, in order to irradiate the object with each point light source element 130-1 to 130-8 by sharing a predetermined image capturing range, the point light source elements 130-1 to 130-8 have been disposed apart from each other, as shown in FIG. 23. Also, in order to supply the light of predetermined uniform intensity to the imaging range, the point light source elements 130-1 to 130-8 have been disposed nearer to the object than the photoelectric conversion device 122, as shown in FIG. 24 (see International Patent Publication No. WO 2004/088588, FIGS. 1 and 6).
Further, there has also been proposed a method for obtaining illumination having spread light to a certain extent by use of a ring-shaped light guide member. According to the above method, a slope notch is provided on the incident side of the ring-shaped light guide member, and light from the point light source is reflected at the slope notch to a spiral direction of the ring, so as to guide the light to the ring spiral direction, and the light is output from an upper face of the ring, and thus a certain range of ring-shaped illumination is produced (see Japanese Unexamined Patent Publication No. 2000-207916, FIGS. 4, 6, 7 and 10).
In the above conventional image capturing apparatus, as described earlier, the point light source elements 130-1 to 130-8 are disposed apart from each other, and nearer to the object than the photoelectric conversion device 122, as shown in FIG. 24. Therefore, it is difficult to miniaturize the image capturing apparatus. Also, there is a restriction when incorporating the image capturing apparatus into equipment.
Further, as also shown in FIG. 24, the point light source elements 130-1 to 130-8 and the photoelectric conversion sensor 122 are disposed in different positions in the height direction of the apparatus. Therefore, a printed circuit board 132 for mounting the point light source elements 130-1 to 130-8 and another printed circuit board 126 for mounting the photoelectric conversion sensor 122 have been provided separately.
As a result, the necessity of two printed circuit boards at the minimum has impeded the cost reduction. Also, the need of two printed circuit boards also causes difficulty in miniaturizing the image capturing apparatus.
Further, because the conventional ring-shaped light guide member aims at ring-shaped illumination, the point light source is changed into a ring light source only. Therefore, it is not suitable to obtain uniform light intensity over a plane having a certain area of an image capturing range.